1. Field of the Invention
The present invention relates to a process for producing a biguanide derivative useful as an intermediate for triazine-type herbicides.
2. Prior Art
As a triazine-type herbicide, JP-A-63-264465 discloses a triazine-type herbicide in which a phenoxyalkylamino group is substituted on a triazine ring, as is shown in the following formula, and this publication describes that the above triazine-type herbicide has remarkable advantages that it has excellent herbicidal effect and exhibits no phytotoxicity on paddy rice. ##STR1##
The phenoxyalkylamino-substituted triazine-type herbicide of the above type is obtained, for example, by reacting a biguanide derivative of the formula, ##STR2## with methyl trifluoroacetate of the formula, EQU CF.sub.3 COOCH.sub.3.
The above biguanide derivative used to obtain the phenoxyalkylamino-substituted triazine-type herbicide is conventionally produced by a method in which a free phenoxyalkylamine is reacted with hydrogen halide to prepare a phenoxyalkylamine salt, and thereafter the phenoxyalkylamine salt is isolated and allowed to react with dicyandiamide. It is suggested in JP-A-63-254465 that an aliphatic hydrocarbon having 7 or less carbon atoms such as n-hexane and n-heptane is used as a solvent for the reaction of a phenoxyalkylamine salt with dicyandiamide.
The defect with the method suggested in the above JP-A-264465 is that the intended biguanide derivative cannot be obtained effectively, especially cannot be obtained under atmospheric pressure, as will be made clear in Comparative Examples to be described later.
Further, as described above, the conventional method of producing a biguanide derivative involves a step of isolating a phenoxyalkylamine salt obtained by a reaction of a free phenoxyalkylamine with hydrogen halide. Therefore, the process is complicated, and the yield of the intended biguanide derivative is inevitably decreased due to the additional complication of the process.
It is therefore a first object of the present invention to provide a process for producing a high-purity biguanide derivative from a phenoxyalkylamine salt at high yields.
It is another object of the present invention to provide a process in which a phenoxyalkylamine salt is prepared from a free phenoxyalkylamine, and thereafter a high-purity biguanide derivative can be produced at high yields in a single operation (one batch) without isolating the obtained phenoxyalkylamine salt.